Software & Apps File Types What Is a Boot File? by Tim Fisher General Manager, VP, Lifewire.com Tim Fisher has 30+ years' professional technology support experience. He writes troubleshooting content and is the General Manager of Lifewire. our editorial process Facebook Twitter LinkedIn Tim Fisher Updated on November 18, 2019 File Types Design Cryptocurrency MS Office Windows Linux Google Drive Apps File Types Backup & Utilities View More Tweet Share Email The word "boot" has different meanings in different contexts. You might be dealing with a file that uses the .BOOT file extension or maybe you're looking for information on when your computer boots up, like the different types of boot up options and how to use bootable files and programs. How to Open .BOOT Files Files that end with the .BOOT suffix are InstallShield files. These are plain text files that store installation settings for the Flexera InstallShield program, which is an application that's used for creating setup files for software installs. Since they're plain text files, you can most likely view the contents of the .BOOT file with a text editor too, like Notepad in Windows or an application from our Best Free Text Editors list. These kinds of BOOT files are sometimes seen stored along with similar installation files like INI and EXE files. What Are Bootable Files? Bootable files have nothing to do with the BOOT file format used by InstallShield. Instead, they're simply files that have been configured to run when the computers boots up. That is, before the operating system has loaded. However, there are two types of bootable files that we need to cover. One set are the files Windows requires in order to boot successfully, that are stored on the hard drive. The other are the bootable files that are stored on other devices that run before the operating system starts. Windows Boot Files When the Windows OS is first installed, certain files are placed on the hard drive that are required to be there in order for the operating system to load, whether in Normal Mode or Safe Mode. For example, Windows XP requires that NTLDR, among other boot files, be loaded from the volume boot record before the OS can start. Newer versions of Windows need BOOTMGR, Winload.exe, and others. When one or more of these boot files are missing, it's common to have a hiccup during startup, where you normally see some kind of error related to the missing file, like "BOOTMGR is missing." See this page for a more comprehensive listing of the boot files required to start different versions of Windows. Other Kinds of Boot Files Under normal conditions, a computer is configured to boot to a hard drive that stores the operating system, like Windows. When the computer first boots up, the proper boot files mentioned above are read and the operating system can load from the disk. From there, you can open regular, non-bootable files like your images, documents, videos, etc. Those files can be opened as usual with their related programs, like Microsoft Word for DOCX files, VLC for MP4s, etc. However, in some circumstances, it's necessary to boot to a device other than the hard drive, like a flash drive or CD. When the boot sequence is properly changed, and the device is configured to be booted from, you can consider those files "bootable files" since they run at boot time. This is necessary when doing things like reinstalling Windows from a disc or flash drive, running bootable antivirus software, testing the computer's memory, partitioning the hard drive with tools like GParted, using a password recovery tool, wiping all the data from the HDD, or any other task that involves manipulating or reading from the hard drive without actually booting to it. For example, AVG Rescue CD is an ISO file that needs to be installed to a disc. Once there, you can change the boot order in BIOS to boot to the optical disc drive instead of the hard drive. What happens next is that instead of the computer looking for boot files on the hard drive, it looks for boot files on the disc, and then loads what it finds; AVG Rescue CD, in this case. To reiterate the difference between boot files and regular computer files, consider that you could install a different AVG program, like AVG AntiVirus Free, onto your computer's hard drive. To run that program, you'd need to change the boot order to launch the hard drive's operating system. Once the computer boots to the hard drive and loads the OS, you'd be able to open AVG AntiVirus but not AVG Rescue CD.